PLC5 to DCS comm failure

I lost my comm from plc5 to dcs bailey infi90. Im using 1770-kf2 as communication interface. KF2 module XMTG goes off and CPU led suddenly flashes red once in a while. I already replaced my kf2 module and recycle the power of plc5 processor but the problem is still there. What else can i do to fixed the problem? Thanks for your help.